Getting to the Bottom of Things

The rear parts of some 375 million year old Tiktaalik fossils have finally been examined in detail, providing evidence that may suggest that they were half way between fish and land animals. This may give us some insight into the evolution of life from water to land. The front parts have previously been studied, but the pelvic bone and tail fin have finally been prepared, allowing for a proper study to be undertaken. Tiktaalik is classed as a tetrapodomorph (transitional vertebrate) which would have been about 2.5m long. It looked like a fish with scales and fins with webbing, but the flat head, and shoulder, forearm and wrist bones are much more like four limbed land animals. They had powerful real fins, supported by a large pelvic girdle - larger than expected for a fish, suggesting that the fins would have been used for both swimming, and for pushing the Tiktaalik along the shallow bottom water, through plants, and maybe even to move between bodies of water. However, its reproduction, sensory system, hunting style and breathing style all suggest that they were dominantly water animals, and they wouldn't have been able to travel any distance on land. The paper discussing all of these findings is very detailed with a lot of "techy" terms, but it ends with a nice reconstruction of Tiktaalik, which allows you to see the detail in the fins.

Reconstruction of Tiktaalic (courtesy of Shubin and others)